The invention relates to the field of insulated pipelines, and in particular to the field of insulated subsea pipelines and subsea insulated pipelines manufactured with pre-cured syntactic elements.
The resistance to flow of liquid products such as oil increases as temperature decreases. This problem can be reduced by using thermally insulated pipelines. However, for offshore pipelines it has usually been more cost effective to reduce the need for insulation by injecting various chemicals into the product.
However, more and more oil and gas is being recovered in deeper, colder water, from subsea production systems where use of viscosity reducing chemicals requires a dedicated line to transport them to the wellhead. This of course is rather expensive.
These prior art insulators worked in the past because the operational depth of the pipeline was rather shallow. However, the oil industry has undergone a rapid movement into deeper water. Several years ago the deepest producing oil well was in approximately fifteen hundred feet of water. However, deep producing oil wells today operate in depths approaching ten thousand feet of water. Significantly, as the operating depth increases these relatively lightweight, low cost, low strength prior art materials become unsuitable. Specifically, the materials can no longer withstand the hydrostatic pressure and become saturated with water, thus undesirably becoming a thermal conductor rather than an insulator.
Syntactic foam is a known insulator for deep-sea pipeline insulation. As known, syntactic foams are composite materials in which hollow structures, such as microspheres are dispersed in a resin matrix. U.S. Pat. No. 6,058,979 entitled xe2x80x9cSubsea Pipeline Insulationxe2x80x9d, assigned to the assignee of the present invention, discloses a semi-rigid syntactic foam for use in deep-sea operations. U.S. Pat. No. 6,058,979 is hereby incorporated by reference. Significantly, the syntactic foam disclosed in this patent is strong enough to support the macrospheres and provide the requisite crush strength for deep-sea operations, while flexible enough to sustain the bending while being laid. Although the insulated pipeline disclosed in this patent has a number of significant advantages, there are certain limitations. For example, shrinkage caused during curing causes internal stresses that can lead to cracks in the insulation. In addition, the amount of material to be cast at one time may be constrained by processing limits.
Therefore, there is a need for an improved subsea insulated pipeline.
Briefly, according to an aspect of the present invention, an insulated pipeline comprises an inner pipe, and an outer poly sleeve co-axial with the inner pipe. The inner pipe and the outer poly sleeve are in spaced relationship to define an annulus. An insulating core within the annulus encases lengthwise the inner pipe, and comprises a plurality of pre-cured syntactic elements. A first binder fills interstices in the annulus.
The pre-cured syntactic elements include microspheres and a second binder. Each of the pre-cured syntactic elements may also include macrospheres.
The pre-cured syntactic elements are preferably extruded. In addition, in one embodiment, the second binder is preferably more rigid than the first binder.
These and other objects, features and advantages of the present invention will become apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings.